Field of the Invention
The present invention relates to a system and a method for estimating a steering torque, and, more particularly, to a system and a method configured for exactly determining and estimating a value of a steering torque applied to a steering wheel by a driver upon failure or removal of a torque detector.
Description of Related Art
Generally, as a power assist steering system configured for reducing a steering torque of a driver upon steering of a vehicle, a Hydraulic Power Steering (HPS) system assisting a steering force of the driver using a hydraulic power generated by a hydraulic pump, and a Motor Driven Power Steering System (MDPS) system assisting a steering force of the driver using an output torque (assist torque) of an electric motor are known in the art.
Among the above, since the MDPS system may control an output of the electric motor configured for steering assist according to a driving condition of the vehicle when performing a steering assist function according to an operation of a steering wheel by the driver, the MDPS provides an improved steering performance and steering feeling than the Hydraulic Power Steering system.
Accordingly, the MDPS system, which may change and control a steering assist force generated by the output of the motor according to a driving condition, is being widely applied to recently released vehicles.
The MDPS system may be configured to include a plurality of detectors, including a steering angle detector configured for detecting a steering angle (column input angle) according to an operation of the steering wheel by the driver, a torque detector configured for detecting a steering torque (a steering wheel torque, a column torque) received through the steering wheel, a vehicle velocity detector configured for detecting a vehicle velocity, a wheel velocity detector, an engine rotation detector, a yaw detector and the like, a controller (MDPS ECU), and a steering motor (MDPS motor).
In the above configuration, the controller is configured to receive and obtain a steering input information related to the driver, including the steering angle, a steering angular velocity, the steering torque and the like, from the detectors and a vehicle status information, including the vehicle velocity, the wheel velocity, the engine rotation, the yaw rate and the like, to control an operation and an output of the steering motor.
Herein, the steering angle indicates a position of the steering wheel and the steering angular velocity may indicate a value of the angular velocity of the steering wheel which is obtained through a separate detector, or generated from a differential signal of a signal of the steering angle (a signal of the steering angle detector), and the steering torque indicates a torque applied to the steering wheel by the driver, that is, an input torque of the driver.
At the present time, the controller is configured to control an operating force (output) of the steering motor according to the vehicle velocity and generates a torque adjusted for steering assist (hereinafter, referred as to as ‘assist torque’), and increases the output of the motor so that the driver may lightly operate the steering wheel at a low velocity and reduces the output of the motor so that the driver may heavily operate the steering wheel at a high velocity, thus obtaining a driving safety of the vehicle.
At a high velocity driving of the vehicle, since a risky situation may occur even by a slight operation of the steering wheel when the steering wheel is very light, there does not come a driving stability. Accordingly, a stable operation of the steering wheel may be achieved by changing a characteristic of the steering assist according to the vehicle velocity and assisting to allow the driver to more heavily operate the steering wheel at a high velocity driving state.
Generally, the output of the steering motor assisting the steering force of the driver is generated by controlling, in the controller, an electric current of the motor (amount of the electric current for assist control) applied to the steering motor.
At the present time, the controller is configured to determine, as tuned, an amount of the electric current corresponding to a value of the output (a value of the assist torque) which is determined based on information collected in the vehicle, that is, the steering input information related to the driver and the vehicle status information, and applies the determined value to the steering motor, and generates the assist torque, which is a force for assisting the steering force of the driver, through the operation of the motor.
In the above steering system, a configuration for delivering the steering force of the driver applied through the steering wheel and the steering assist force generated by the motor includes a steering column disposed on a lower portion of the steering wheel, a gear box converting a rotational force delivered from the steering column into a direct force and changing a direction of a tire, and a universal joint delivering the rotational force delivered to the steering column to the gear box.
Herein, the gear box includes a pinion gear receiving the rotational force from the universal joint and a rack bar with a rack engaging the pinion gear formed thereon, and the rack bar performs a direct motion from side to side by the rack upon rotation of the pinion gear.
At the present time, a force generated by the direct motion of the rack bar is delivered to the tire through a tire rod and a ball joint, and changes a direction of the tire.
Meanwhile, the MDPS system utilizes the steering torque (column torque) detected by the torque detector configured to control an operation and an output of the steering motor, and FIG. 1 is a view of generating a value of the assist torque using the steering torque detected by the torque detector for steering assist.
As shown in FIG. 1, the MDPS system generates the value of the assist torque using the steering torque detected by the torque detector and controls the operation of the motor using the generated value of the assist torque.
At the present time, the MDPS system controls an electric current applied to the motor, that is, the electric current of the motor, using the value of the assist torque and generates a steering assist force targeted (assist torque by the motor).
However, upon failure of the torque detector, as shown in FIG. 2, since the controller does not know a current torque, the controller may not determine the value of the assist torque. As a result, since the steering assist may not be performed, the driver suddenly loses the steering force while driving the vehicle and therefore may be in a risky situation.
Accordingly, it is necessary to estimate the value of the steering torque received through the steering wheel by the driver and perform an appropriate steering assist.
A method of analyzing or detecting an occurrence of abnormal of a signal or failure in the steering system and a fail-safe control method of controlling the steering system upon detection of failure are disclosed.
According to the related art, upon failure of a torque detector in a MDPS, as shown in FIG. 3, a method of estimating a steering torque using a steering angle and a motor rotation angle detected by detectors 1, 2 and generating a value of an assist torque using the estimated steering torque.
However, the above method estimates twist of a torsion bar from the steering angle and the motor rotation angle and estimates the steering torque, and in the method, an error may be largely occurred due to estimation of the twist of the torsion bar and it is not applicable to a type of DC motor that does not have a motor rotation angle detector 2.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.